textproduct: Rapid City

KEY MESSAGES

- Widespread critical fire weather conditions expected Wednesday afternoon.

- Scattered thunderstorms over south central South Dakota Wednesday afternoon and evening may produce strong wind gusts.

- Cool, breezy unsettled weather expected Thursday through the weekend.

DISCUSSION

(This Evening Through Tuesday) Issued at 110 PM MDT Tue Apr 21 2026

Water vapor analysis shows upper ridging across the central CONUS, while a large stacked low just offshore the CA/OR coast slowly moves eastward. At the surface...departing surface high is bringing S/SE return flow to western SD. Temps are rising through the 70s into the 80s across the plains. Quiet weather is expected for the rest of today and tonight, with overnight lows in the 40s/50s. The large Pacific system will slowly continue eastward, eventually affecting our area for the second half of the week. The upper low is progged to break up through Thursday as a second wave digs down the backside of the trough toward Friday and the weekend. With lots of changing dynamics, there is low confidence and consistency with many details/forecast elements over the next several days. Backing up to Wednesday, warm air advection will continue overnight through the daytime hours tomorrow bringing very warm air to the region. Temperatures across the western/central SD plains are expected to reach the 90s...mainly east of the Black Hills. Some locations could even see temps creep into the mid 90s, which would be approaching daily (and even monthly) records. Southerly flow will persist across central SD, with dewpoints in the low 40s. Then models show a dryline pushing into SW SD during the afternoon with SW winds behind it. The main non-fire weather concern tomorrow will be the development of thunderstorms along this line. Some storms may initiate somewhere in the SCentral SD vicinity in the later afternoon/early evening, then ramp up a little as a cold front pushes in from the west later Wed evening (after 03z). With how dry the boundary layer will be, LCLs will be well above 10kft. Instability above that level, however, will be limited to 500-800 J/kg. Hail is not expected to be much of a concern, but inverted V soundings suggest strong wind gusts will be possible. Then a second surge of (elevated) convection with the front itself could bring better chances for stronger winds, especially as the lower atmosphere mixes with the cold air advection. Will keep an eye on this. For Thursday, models continue to back off QPF amounts and winds as the system trends farther north and the CWA sits within the dry slot. Snow amounts across the Black Hills late Thursday/Friday should be limited to an inch. Winds on Thursday have dropped to within advisory criteria, but this could be further decreased with future runs. Mostly cloudy skies, cooler temperatures, and chances of rain/snow continue through the rest of the week into the weekend as the secondary shortwave digs down the backside of trough, keeping it over the region.

AVIATION

(For the 18Z TAFS Through 18Z Wednesday) Issued At 1136 AM MDT Tue Apr 21 2026

VFR conditions are expected through the TAF period.

Changes in flying conditions are mainly centered around wind speed and direction changes due to an incoming low pressure center and frontal passage.

For most of the TAF period, the area will remain ahead of the front. So wind directions will be out of a general south to southeasterly direction. As the front tracks through from west to east, the winds will swing to out of a westerly direction tomorrow. As far as timing goes, NE WY could start the shift around around 14 to 16z. Western SD could start the shift around 17 to 19z. West to northwest winds will last through the rest of the week.

Wind speeds will respond to the low and front by increasing and staying elevated, even after the front tracks through. Speeds will start to increase, in response to the front, beginning around 15z. Gusts upwards of 30 to 40 mph are possible behind the front with a brief lull in the speeds Wednesday night. Wind speeds will pick back up again Thursday with gust potential higher than what we'll see on Wednesday.

FIRE WEATHER

Issued At 110 PM MDT Tue Apr 21 2026

Widespread critical fire weather conditions are expected for Wednesday. Temperatures will climb into the 80s to 90s across much of western SD, with humidities as low as 10%. Southerly winds will also pick up across the region ahead of an approaching cold front (gusts of 30-45 mph). Thunderstorms are possible Wednesday afternoon. These storms aren't expected to produce much rain but will be capable of lightning and strong, erratic wind gusts of 50+ mph.

A cold front will cross the region early Thursday bringing much cooler temps, rising humidities, and breezy northwest winds (gusts of up to 50 mph across NW SD).

UNR WATCHES/WARNINGS/ADVISORIES

SD...Red Flag Warning from 10 AM MDT /11 AM CDT/ to 8 PM MDT /9 PM CDT/ Wednesday for SDZ319>335. WY...Red Flag Warning from 10 AM to 8 PM MDT Wednesday for WYZ314>318.